1. Field
The presently disclosed subject matter relates to semiconductor light-emitting devices, and more particularly to surface mount semiconductor light-emitting devices with a high reliable structure, which can prevent causing cracks in encapsulating resins during/after a reflow soldering process when the semiconductor light-emitting devices are mounted on a mounting circuit board.
2. Description of the Related Art
Semiconductor light-emitting devices, in which a part of the light emitted from a semiconductor light-emitting chip is converted into light having a different wavelength by a phosphor and in which a mixture light including the light having the different wavelength mixed with the light emitted directly from the semiconductor light-emitting chip is emitted, have been known as semiconductor light source(s) for various lighting units. In this case, the semiconductor light-emitting devices are usually provided with a wavelength converting material including a phosphor around the semiconductor light-emitting chip such as an LED chip, etc.
Meanwhile, in various semiconductor light-emitting devices, surface mount devices are frequently used for an electronic device such as a mobile phone, a personal computer and the like because they are small, light and can be directly mounted along with other electronic parts on a mounting circuit board in a reflow soldering process. Conventional semiconductor light-emitting devices of a surface mount type, for example, are disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2001-127345) and No. 2 (U.S. Pat. No. 8,115,106).
FIGS. 18a and 18b are a top view and a side cross-sectional view taken along line A-A in FIG. 18a showing a conventional semiconductor light-emitting device of the surface mount type, which may be used as a light source for a back light unit of an liquid crystal display (LCD) apparatus and the like and which is disclosed in Patent Document No. 1, respectively.
The conventional semiconductor light-emitting device includes: a mounting board 82 having a cavity 83 made by attaching a first board 80 having a top surface and an opening on a second board 81, and formed in a tabular shape; a first conductor pattern 84 formed continuously in the cavity 83, which is composed of the opening of the first board 80 and a part of the top surface of the second board 81, which is exposed from the first board 80, and extending from the cavity 83 toward the top surface of a side surface the first board 80 and a side surface and a bottom surface of the second board 81; and a second conductor pattern 85 being formed from another top surface of the first board 80 toward another bottom surface of the second board 81 so as to separate from the first conductor pattern 84.
In addition, the semiconductor light-emitting device also includes: a semiconductor light-emitting chip 86 having a top electrode and a bottom electrode mounted on the first conductor pattern 84, which is located on a bottom surface of the cavity 83, the bottom electrode thereof being electrically connected to the first conductor pattern 84, and the top electrode thereof being electrode connected to the second conductor pattern 85 via a bonding wire 87: and a transparent resin having a light-emitting surface being disposed on a part of each of the first conductor pattern 84 and the second conductor patted 85 so as to encapsulate the bonding wire 87 therewith, and formed in a dome shape, and the light-emitting surface thereof exposed from a top surface of the transparent resin 88 as a light-emitting surface of the device.
When the conventional light-emitting device is used as a light source for the back light unit of the LCD apparatus, the semiconductor light-emitting device should emit light having a substantially white color tone in general to show eye-friendly displays on the LCD apparatus. In this case, the conventional light-emitting device may further include a wavelength converting material 89 including a phosphor, which is located in the cavity 83 so as to cover the semiconductor light-emitting chip 86 therewith, and thereby may emit a wavelength converted light having the substantially white color tone.
For example, when the semiconductor light-emitting chip 86 is a blue LED chip emitting blue light and the wavelength converting material 89 is composed of a transparent resin including a yellow phosphor, which can emit a yellow light upon being excited by the blue light emitted from the blue LED chip, the semiconductor light-emitting device can emit substantially white light from the light-emitting surface of the transparent resin 88, by an additive color mixture of the excited yellow light emitted from the yellow phosphor and a part of the blue light emitted from the blue LED chip. Accordingly, the conventional semiconductor light-emitting device may be used as a light source for the back light unit of the LCD apparatus.
In a structure of the conventional semiconductor light-emitting device, as the transparent resin 88 including the light-emitting surface of the device, a transparent material having a high permeability such as an epoxy resin should be used. A transparent resin having a high thermal resistance such as a silicone resin would be use as the transparent resin for the wavelength converting material 89 so as to prevent a degradation of the wavelength converting material 89, which is caused by a heat generated from the semiconductor light-emitting chip 86 during operation.
However, a thermal expansion coefficient of the epoxy resin used to cast the transparent resin 88 may be extremely different from that of the silicone resin, which is used for the wavelength converting material 89. Specifically, the thermal expansion coefficient of the silicon resin, which is generally used as the transparent resin for the wavelength converting material 89, may be considerably larger than that of the epoxy resin, which is used as the transparent resin for the transparent resin 88.
Hence, when the semiconductor light-emitting devise of a wavelength converted type using the above-described structure is directly mounted along with the other electronic parts on the mounting circuit board in a reflow soldering process, the wavelength converting material 89 including the silicone resin, which is disposed in the cavity 83, may expand due to a heat of the reflow soldering. Said thermal expand may be applied toward the transparent resin 88, which is made from the epoxy resin having a small thermal expansion coefficient, because the first conductor pattern 84 is made of a solid metallic material and is sustained by a solid board of the mounting board 82.
Then the transparent resin 88 may be boosted in an upward direction thereof from the cavity 83 including the wavelength converting material 89 by a stress of the thermal expansion, and the thermal expansion stress may enlarge toward the transparent resin 88 in a radial fashion. Accordingly, a peeling may occur on a boundary between the transparent resin 88 and an annular section 84a of the first conductor pattern 84, which is located around an outer top edge of the wavelength converting material 89, and between the transparent resin 88 and another section of the first conductor pattern 84, which directly contacts with the transparent resin 88.
The peeling may extend from the annular section 84a in an outward direction of the first conductor pattern 84 along a connecting pattern 84b, which connects the annular section 84a to an electron portion of the first conductor pattern 84 that extends underneath the mounting board 82 as shown in FIG. 18a and FIG. 18b. After that, at the peeling portion where occurs on the boundary between the transparent resin 88 and the annular section 84a and the other section of the first conductor pattern 84 in the semiconductor light-emitting device mounted on the mounting circuit board, a fluid, a saline matter, a dirt, a dust and the like may enter toward the wavelength converting material 89.
In worst case, the fluid and the like may finally get to the semiconductor light-emitting chip 86 while the semiconductor light-emitting device has been used under various severe environments for a long time. As a result, the peeling may cause a degradation of optical characteristics such as a reduction of a light-emitting intensity, color variability, a light-emitting failure and the like, and finally may cause a failure of the semiconductor light-emitting device. Therefore, the above-described structure of the device may cause a degradation of a reliability of the semiconductor light-emitting device.
Such a peeling may be easy to occur when a Pb-free solder having a higher melting point of approximately 260 degrees centigrade than a tin-lead solder having a melting point of approximately 200 degrees centigrade is used in the reflow soldering process. Accordingly, the conventional semiconductor light-emitting device may be difficult to be used as a light source such that requires a high reliability, for example, when the semiconductor light-emitting device is used under various severe environments for a long time as a light source for automobile parts such as a position lamp, a room lamp, etc.
The above-referenced Patent Documents are listed below, and are hereby incorporated with their English abstracts in their entireties.    1. Patent Document No. 1: Japanese Patent Application Laid Open JP2001-127345.    2. Patent Document No. 2: U.S. Pat. No. 8,115,106.
The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, embodiments of the disclosed subject matter can include small semiconductor light-emitting devices having a high reliable structure, which can prevent causing cracks in encapsulating resins even when the semiconductor light-emitting devices are mounted on a mounting circuit board under a high temperature in a reflow soldering process, and which can emit a wavelength converted light having a high light-emitting efficiency and a high light-harvesting efficiency. The disclosed subject matter can also include a semiconductor light-emitting device using a plurality of semiconductor light-emitting chips that can be used for wavelength-converting light having a high light-emitting efficiency and a high light-harvesting efficiency.